Free Traffic Legal Advice

Today I received a notice of intended prosecution for the above offence.
When setting off from traffic lights in a 3 lane junction and turning right, I moved from the middle lane to the inside lane. I was unaware of a car in the inside lane coming up from behind and may not have signalled. The car was forced to break (I’m assuming: I don’t recall any squealing tires etc). The driver leaned on his horn, I apologised by flashing my hazard lights, he mouthed some words, which I couldn’t hear, and drove off.
Dash cam footage was included with the notice.
According to the internet, I could face anything from a £100 fine and 3 points to ultimately a court summons resulting in £5000 and disqualification.
Where along this scale is my punishment likely to fall?
Thanks in advance for any replies.

You do, of course, have the option of pleading not guilty as well, whether that may be wise depends on what the footage shows. It will cost more in costs if convicted.

The foreshortening on a dash cam can make things look worse.